As shown in FIG. 4, a portable combustion type power tool 90 generally includes a housing 2, a cylinder 20, a piston 25, a driver blade 28, a chamber head 13, a combustion chamber frame 11, a canister housing 49, a fan 14, an ignition plug 15, and a trigger switch 6. The housing 2 contains various components. The cylinder 20 is provided in the housing 2. The piston 25 is slidably movable in the cylinder 20 in an axial direction thereof. The driver blade 28 is fixed to the piston 25 and drives fasteners into a workpiece W as the piston 25 moves. The chamber head 13 is spaced from an end of the cylinder 20, and is secured to the housing 2. The combustion chamber frame 11 is provided in the housing 2 and is movable in the axial direction while sliding on an outer circumferential surface of the cylinder 20. The combustion chamber frame 11 is contactable with the chamber head 13 in accordance with the axial movement to provide a combustion chamber 26 in combination with the chamber head 13 and piston 25. The canister housing 49 is provided in the housing 2 and is adapted for containing a gas canister 5. A gas injection port 18 is formed in the chamber head 13 for injecting a combustible gas from the gas canister 5 into the combustion chamber 26. The fan 14 is provided in the combustion chamber 26. The ignition plug 15 ignites the mixture of air and the combustible gas injected into the combustion chamber 26 through the gas injection port 18. The trigger switch 6 is secured to the housing 2.
The combustion type power tool 90 further includes an ignition control device 110 (see FIG. 5). As shown in FIG. 5, the ignition control device 110 includes a control circuit 102 electrically connected to the trigger switch 6. The control circuit 102 transmits a driving signal to the ignition plug 15 for generating a spark thereat when the trigger switch 6 is operated. As shown in a block diagram of FIG. 5, in the ignition control device 110, a secondary battery 100 such as a nickel-cadmium battery supplies power, and the trigger switch 6 and a head switch 101 transmit an on-signal and an off-signal to the control circuit 102. The control circuit 102 is also adapted to control a fan driver circuit 103 and an ignition circuit 104 and to drive a display circuit 105.
In the combustion type power tool 90, nail driving depth into the workpiece can be adjusted by a protruding length of a push lever 10 protruding from a nail-driving port of a tail cover 9 that is provided below the cylinder 20. When the push lever 10 is pushed onto the workpiece W, a coupling member 12 moves in interlocking relation to the movement of the push lever 10, so that the coupling member 12 pushes the combustion chamber frame 11 upwards. As a result, the combustion chamber frame 11 abuts on the chamber head 13, whereupon the combustion chamber 26 is sealed from outside.
In synchronism with the movement of the coupling member 12, a pushing means including a projecting member 16 and an L-shaped lever 50 is also moved. That is, the projecting member 16 moves in synchronism with the movement of the coupling member 12, so that the L-shaped lever 50 is pivotally moved to push the injection nozzle (injection rod) 39 of the gas canister 5 set in the canister housing 49. The combustible gas is thus injected from the injection nozzle 39 into the combustion chamber 26. In the combustion chamber 26, the combustible gas is stirred by the fan 14 driven by a control circuit 102 and a fan driver circuit 103, both shown in FIG. 5. The combustible gas is therefore mixed with air, forming air-fuel mixture. In this condition, the control circuit 102 and an ignition circuit 104, both shown in FIG. 5, are operated, causing the ignition plug 15 to generate a spark in the combustion chamber 26. The air-fuel mixture is combusted in the combustion chamber 26, generating a force that can drive fasteners, such as nails, into the workpiece.
The combustion type power tool 90 need not have a compressor, unlike conventional nail gun that uses compressed air as a drive source. The power tool 90 can therefore be transported to a construction site more easily than the conventional nail gun. In addition, since the power tool 90 has a built-in power supply such as a secondary battery, the power tool 90 requires no other power supplies including the commercially available power supply. Therefore, the power tool 90 is advantageous in operability among a portable tool.
The above-described combustion type power tool is disclosed in, for example, Japanese Patent Publication Nos. H01-34753, H04-48589, H03-25307, H04-11337, S64-9149, and H07-36985.
In the above-described conventional combustion type power tool 90, the gas canister 5 detachably held in the canister housing 49 is usually still retained in the canister housing 49 even after the end of a work at a working place such as a construction site. If the push lever 10 is unintentionally or accidentally operated while the gas canister 5 remains set in the tool 90, the push lever 10 will move upwards because the lever 10 is merely biased by a coil spring 37. As the push lever 10 moves, the coupling member 12 coupled to the push lever 10 drives the pushing means including the link member such as the lever 50 and the like, via the combustion chamber frame 11. Consequently, the injection nozzle 39 of the gas canister 5 is pushed, and the combustible gas is unnecessarily injected into the combustion chamber 26. The combustible gas is inevitably wasted. In addition, particular attention must be drawn to accidental ignition of the combustible gas thus injected wastefully.
While the combustion type power tool 90 is left unused, electric power is supplied to the ignition control device 110 (see FIG. 5) even if no unintentional operation of the push lever 10 takes place, as long as the battery 100 remains set in the power tool 90. That is, the control current flows at all times to monitor the on- or off-state of the trigger switch 6 and head switch 101. In this case, the electric power is wasted.
Therefore, the gas canister 5 and the battery 100 must be removed from the tool 90 after the end of work. However, pulling the battery (battery pack) from the tool every time the work is ended is cumbersome. In many cases, the worker lefts the battery set in the tool. If the battery remains in the tool for a long time while the tool remains unused, the battery voltage will be dropped due to discharge, particularly in an ordinary battery such as a nickel-cadmium battery. As a result, the tool may not be driven when necessary. Further, a service life of the battery will be shortened if the battery is fully discharged or over-discharged. In the latter case, the battery must be replaced by a new battery.